Rendering a still image (not animation) with motion blur
Why do you need to create an animation?
Because you need transformation, both in space and time.

For motion blur to exist there has to be a notion of before and after. An object (or the camera) was in one place in frame 1 



and is in a different place in frame 3.



Depending on the distance the objects moved, and the shutter speed set in the motion blur settings, you might see the movement in frame two represented as a blurred image.



You certainly don't need to render an animation (frames 1, 2 and 3) you can render just frame 2 and the motion blur should be there as a still image.

Notice that in this example even in frames 1 and 3 there is some motion blur because of the magnitue of the transformation from frame to frame(relative to the shutter speed).

If we were to render frame 0 and 4 the cube would appear static because there is no transformation from frame to frame anymore.